Heretofore images of high quality have been produced by thermal printers. In a typical thermal printer an image is formed in three passes. First a dye donor having color such as yellow is placed in dye transfer relationship with a receiver and then the dye donor is heated in a pattern corresponding to the yellow portion of an image to be completed. Thereafter, cyan and magenta portions of the image are formed in a similar fashion. The completed color image on the receiver is continuous tone and in many cases can rival photographic quality.
In one type of thermal printer which prints colored images, a donor contains a repeating series of spaced frames of different colored heat transferable dyes. The donor is disposed between a receiver, such as coated paper, and a print head formed of, for example, a plurality of individual heating resistors. When a particular heating resistor is energized, it produces heat and causes dye from the donor to transfer to the receiver. The density or darkness of the printed color dye is a function of the energy delivered from the heating element to the donor.
Thermal dye transfer printers offer the advantage of true "continuous tone" dye density transfer. This result is obtained by varying the energy applied to each heating element, yielding a variable dye density image pixel in the receiver.
Thermally printed images are used in a number of different applications. In one of those applications, so-called "sticker prints" are made on a receiver and arranged so that they can be peeled off and individually pasted onto another surface. However, these stickers are not used in situations which require that they be "authentic". By use of the term "authentic" is meant that the image can indicate to a viewer or a reader with a high degree of certainty that the image has not been counterfeited.